Device and method of productive formation selective processing

ABSTRACT

There are proposed a method for selective processing of a productive formation and a device for implementation thereof coupled with a tubing. The device is lowered to the formation’s lowest interval and fixed therein. Working fluid is supplied into the device’s hydraulic fracturing port, the interval is isolated with sealing elements, and hydraulic fracturing is executed. An annular gap is flushed with flush fluid, the lower packer is activated and debris is washed out of the gap through a hydraulic fracturing port. The device is turned to the transport position. The tubing is moved shifting the device’s hollow rod and flushing holes are opened. Flush fluid is then fed into the tubing, the sealing elements are activated and debris is washed out of the gap’s lower area pushing the mixture along the device’s inner cavity into the well. Then the device is moved to the next interval for further processing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of aninternational application PCT/RU2021/00362 filed on 23 Aug. 2021,published as WO/2022/039627, which international application claimspriority of a Russian Federation patent application RU2020128064 filedon 21 Aug. 2020.

FIELD OF THE INVENTION

The invention relates to mining and is used to repair and operate oilwells. It is designed for productive formation selective processingwithin one tripping with real-time annular space flushing during wellwork.

BACKGROUND OF THE INVENTION

One of the main problems affecting the efficiency of repair andoperation of oil wells is the one occurring during their processing -downhole equipment sticking. It is often the result of the tool jammingwhen moving up the well, because the annular space between the downholeequipment and the production string is sprinkled with various solids, inparticular, compressed proppant. It is difficult, time-consuming andexpensive to eliminate accidents caused by sticking.

To solve this problem, well-known preventive technologies are used,which capture and remove solids from the well, including the adjacentareas.

One of the ways to prevent an accident in the well due to the downholeequipment sticking is to ensure high-quality flushing of the cavitiesbetween the equipment and the production string, especially in the areaof the productive formation, as well as the internal cavities of theequipment used for process fluids.

To remove solids (granular debris or formation sand) from the annulus,tools containing various filtration devices, trapping elements andstorage tanks are used.

A method of oil-well jet pump operation is to be mentioned, whichinvolves productive formation area clean-up performed after hydraulicfracturing using oil-well jet pump (patent of the Russian Federation No.2273772, published 10.04.2006, bulletin 10). According to this method,downhole equipment being part of a jet pump with a stepped throughchannel in its casing, as well as a packer with a through channel and ashank with an inlet funnel positioned below the jet pump are descendedinto the well on the tubing string (hereinafter referred to as tubing).Then the packer positioned above the productive formation is unpacked.Next, a blocking insert with a central through channel is installed inthe stepped through channel of the jet pump, and frac fluid or a mixtureof frac fluid with chemical reagents is injected into the productiveformation. After that, the blocking insert is removed and lifted to thesurface, and a flexible tube is lowered through the tubing into the wellthrough the seal assembly, so that the tube could be moved. The sealassembly is installed while lowering the flexible tube in the steppedthrough channel of the jet pump. The lower end of the flexible tube isinstalled below or at the level of the lower perforation interval of theproductive formation.

Next, a working liquid medium is fed into the nozzle of the jet pumpthrough the annular space of the well. The productive formation isdrained by creating a depression on the productive formation. At thesame time or after a stable depression is created, liquid for washingthe well bottom is fed through the flexible tube. The ratio between thefluid pressure in the flexible tube and the fluid pressure in theannular space of the well is maintained at (Pr:Pp)≤0.98.

After pumping fluid of a volume equal to at least two volumes of fracfluid or a mixture of frac fluid with chemical reagents out of theproductive formation, the fluid stops to be fed into the flexible tubefor flushing the bottom of the well.

No sooner than after 5 minutes, the supply of the working liquid mediumto the nozzle of the jet pump is stopped and the flexible tube with theseal assembly is removed from the well. Then, using a jet pump,hydrodynamic and geophysical studies of the productive formation arecarried out to assess its productivity. After that, the well is placedinto operation.

The well jet device used to implement the described method comprises apacker and a through channel on a tubing string, as well as a jet pump,in the body of which an active nozzle and a mixing chamber with adiffuser are arranged. In addition, the jet pump is equipped with astepped through channel. Below the jet pump, there is a shank with aninlet funnel. A seal assembly or, alternatively, a blocking insert isinstalled in the stepped through channel. A flexible tube is put throughthe seal assembly. The lower end of the flexible tube is installed belowor at the level of the lower perforation interval of the productiveformation. The well jet device is placed in the well in such a way thatthe jet pump and packer are located above the productive formation.

The disadvantage of this method and the well jet device itself is thehigh probability of emergency extraction from the well in the event ofjamming due to the sprinkling of mechanical debris in the annular spacebetween the tool and casing. Cleaning and extracting solids, inparticular, flushing the annular space from the proppant, is notperformed according to the method described in the patent. Due to thepacker being sprinkled on top, which cannot be avoided, the design ofthe jet device does not allow fluid to flow in a reverse direction towash debris out from the well, for example, through the annulus space.

Another disadvantage of this system is that it is impossible to use whenprocessing several intervals of the productive formation within onetripping, since after washing the bottom of the well, the device isimmediately lifted to the surface.

The patent US 10280713 (published 2019-05-07) describes systems andmethods for managing debris, including proppant, in the well, providingflushing of the annular gap between casing and the downhole tool.

These technical solutions are aimed at the passive removal of large andsmall debris and precipitated fluid chemicals from a rig’s circulationsystem and blow out preventers at the wellhead, as well as at preventingsand from reaching the annular space between casing and the downholetool. The description to the patent contains information about thevariants of separate assemblies of the annular space cleaning system inthe wellbore, which contains a reversing tool installed on the tubingand debris traps with a built-in filter. The system can also be equippedwith a washpipe where debris traps may be located being an indicator ofcleaning efficiency.

The trap consists of two separate assemblies - the upper and lower onespositioned in the workstring at some distance from each other. The upperassembly comprises a screen resembling a sieve, a bull plug and a 3-wayadapter. The lower assembly comprises a screen, a 3-way adapter and aball check valve. The upper and lower assemblies are fixed in theworkstring using known means of connection. The trap works together withthe sand control tool in the well.

The process fluid with the proppant enters the tubing for hydraulicfracturing, while the proppant begins to accumulate in the annular spacebetween the tool and casing. The fluid passes through the screen builtinto the tubing and enters the washpipe. Then the fluid passes throughthe lower assembly of the trap and the ball valve, and enters thewashpipe area between the assemblies and then the upper assembly of thetrap. Moving forward, the fluid is additionally filtered in the trapassemblies. This prevents the further spread of the proppant. Theproppant is separated from the fluid by the filter of the lower assemblyand is blocked by the ball check valve. When removing equipment from thewell, the degree of contamination is determined by the amount ofproppant in the washpipe between the trap assemblies. If not removingequipment from the well, it is the loss or reduction of fluid on itsreturn to the surface which may indicate the degree of contamination.

The reversing tool is designed to carry fluid and debris out of thewell, especially when there are large annular cross-sectional areas. Thetool permits reverse circulation of the riser at reduced pump rateswithout compromising debris carrying capacity. The reversing toolconsists of a cylindrical component with cup sealing elements thathermetically separate the casing and create two separate annular gaps:one above and one under the sealing elements. In addition, thecylindrical element is equipped with an internal partition forming twochannels in the internal cavity of the tubing. One channel isdescending, the other is ascending. Through the descending channel, theflow of fluid or other material is removed from the tubing into theannular space under the sealing element. Through the ascending channel,the flow of fluid or other material rises along the tubing below thesealing element and is removed into the annular space above the sealingelement. The flow rate decreases, since the cross-sectional area of thetubing is smaller than the annular space. The annular space above thesealing element can be used for collecting debris that cannot be carriedby the flow at a reduced speed, while debris collectors should notprevent the flow from flowing at a technological speed.

The reversing tool is part of the fluid circulation system. The fluidflows from the tank through the suction line to the pump, which belongsto the surface system. The pump moves the flush fluid through thepipeline to the upper tubing string above the cup sealing element.

The flush fluid flows down the upper part of the tubing to the reversingtool, where it is diverted to the annular space under the cup sealingelement. The mixture of the flush fluid and debris continues to flowdown the annular space to the bottom of the well and returns to thetubing again. Next, moving up the tubing, the filtered mixture reachesthe reversing tool and again diverts and enters the annular space abovethe cup seal. Then, flowing up the upper part of the tubing, the flushfluid enters the tank. Thus, a full cycle of the flush fluid circulationis performed. The reversing tool can continuously operate for more thantwo years, performing more than 4000 cycles during its lifetime.

There is an alert system comprising pressure gauges, which monitor thepressure differential and indicate a risk of blockage to alert a welloperator that the traps have filled or contain significant amount ofdebris.

The disadvantage of this system is the limited scope of use, mainly inoffshore wells, and does not involve simultaneous technologicaloperations for processing productive formations. In addition, theoperation of the system is based on multiple filtration stages, andcontains complex equipment for washing these devices that should bereplaced periodically.

The closest to the claimed technical solution is the invention presentedin the patent US 10494900 (published 2019-12-03), which presents optionsfor a well stimulation system performing hydraulic fracturing with aflushing device and describes a method for flushing the annulus, inparticular in the area of the annular gap between the string and thewellbore.

The composition and arrangement of the main components of the system aresimilar for all the versions presented in the patent and include ananchor installed on the tubing (from bottom to top), lower packer,hydraulic fracturing unit, upper packer, mechanically operated valve,sand control assembly and pressure activated injection assembly. Belowthe anchor there is a valve that is closed during hydraulic fracturingand a hole for removing excess fluid.

The anchor fixes the device to the wellbore and can be installed byaxial movement up and down. The upper and lower packers are designed toisolate the area of the productive formation. The mechanically operatedvalve is part of the sand control assembly and participates in creatinga pressure difference in the annulus below the sand control assembly toensure the annular gap flushing. The sand control assembly is positionedabove the hydraulic fracturing unit and is designed to remove theextracted sand and gravel from the annulus when moving to anotherprocessing zone or to the surface. A flushing device is used togetherwith the sand control assembly during the annular gap flushing. Itprovides hydraulic communication with the annular space in the annulargap zone through radial ports.

In addition, to ensure a significant pressure difference determined bythe condition in the wellbore, for example, when the pressure of theflushing fluid exceeds 2-5 times the pressure of the hydraulicfracturing process fluid, the sand control assembly is additionallyequipped with a check valve and one or more additional packers.

The patent presents three versions of the flushing device, one of whichcan be activated several times, which ensures flushing of the annulargap when processing several productive formations within one tripping.

The flushing device is located above the hydraulic fracturing unit, isconnected to the valve and opens when the flushing fluid is fed at anappropriate pressure, which is significantly higher than the hydraulicfracturing pressure. That is why the device is closed during hydraulicfracturing.

The flushing device comprises a sliding sleeve installed in the housing,a piston and a return spring. A spring force from a return springopposes the net pressure force exerted on the net piston area. Radialports are made in the housing, blocked by the piston when the flushingdevice is closed. Radial ports have nozzles to ensure the jet flows at agiven angle into the wellbore to flush the annular space in differentdirections.

The advantage of this version of the flushing device is that it returnsthe sliding sleeve and covers radial ports when the pressure on thepiston is released after the annular gap is flushed.

The system is also equipped with a release mechanism that activates anddeactivates the packers sealing the productive formation area and thehydraulic fracturing unit.

The release mechanism is made in the form of a housing, which is part ofthe system, with an axially movable inner sleeve inside. The innersleeve is provided with a radial port. Between the housing and the innersleeve, there is a removable sleeve with axially extending conduitshydraulically connected to the annular space.

When the system is idling, the inner sleeve is in the working position,while the packers sealing the productive formation area and thehydraulic fracturing unit are not active. The radial port of the innersleeve is closed by a removable sleeve. The position of the inner sleeveensures the passage of fluid through the piston inside and closes thehydraulic connection with the annulus through the radial ports in thehousing. The removable sleeve is fixed within the housing by a retainer.

When pressure is applied to the piston inside, the inner sleeve,overcoming the force of the return spring, performs an axial movementuntil the hydraulic connection is restored through radial ports in theinner sleeve and in the housing, which communicate with the spacebetween the housing and the sleeve. The pressure in the piston insidepartially drops, the spring forces the inner sleeve to return to theidle position. Under the pressure, the retainer moves into the seatwhere it is installed, freeing the removable sleeve. This sleeve coversthe radial port in the housing, maintaining the hydraulic connection ofthe piston cavity with the area between the housing and the innersleeve. The increasing flushing pressure does not exceed the one withwhich the return spring influences the inner sleeve. In this conditionof the release mechanism, the hydraulic fracturing unit is closed, thepackers sealing the productive formation area are not activated.

The system is designed to be used in emergencies when it is impossibleto remove the drilling tool from the well, as the upper packer issprinkled with debris and it is impossible to flush the annular gap inthe annular inter-packer space. This makes it impossible to control theflushing circulation unit and extract the tool from the well. Additionalunits are required to flush the space above the second-from-the-bottompacker.

Another disadvantage of the system is its complicated structure causedby additional elements for various purposes (packers, valves), the useof spring mechanisms for controlling the flushing device, which areprone to instability, changes in elastic properties and subsequentdeformation.

One more disadvantage of the device is the use of high pressures thatexceed the hydraulic fracturing pressure by 2-5 times when flushing.

In the fields of Western Siberia, where the depth of wells can reach3500 m, and the hydraulic fracturing pressure can reach 700 atmospheres,the flushing pressure will be 1400-3500 atmospheres, which issignificantly higher than 1000 atmospheres - the pressure for whichstandard hydraulic fracturing equipment is designed. Using pressureswhich are several times higher than the one of hydraulic fracturingduring annular space flushing requires non-standard wellhead equipment,a non-standard tubing hanger, non-standard pumping equipment forhydraulic fracturing, which significantly reduces the manufacturabilityof the system and limits its scope of use.

OBJECTS AND BRIEF SUMMARY OF THE INVENTION

The objective of the invention is to increase the efficiency of aproductive formation processing within one tripping, reduce the accidentrate and increase the lifetime of the proposed device (herein furtherreferred to as the ‘inventive device’). Typically, a borehole usable inthe mining industry is associated with the productive formation, and awell casing is mounted within the borehole. A tubing (also known as‘tubing string’) is typically inserted into the well casing. An annulusspace is herein defined as a space between an outer surface of theinventive device / tubing and, on the other hand, an inner surface ofthe well casing. The inventive device, essentially coupled with thetubing, comprises: a mechanical anchor, a collar locator, a lowerfeedthrough packer, a hydraulic fracturing port, an upper feedthroughpacker and a centralizer sequentially installed from bottom to top onthe tubing. An inter-packer annular gap is herein defined as a portionof the annulus space located between the outer surface of said inventivedevice and the inner sidewall surface of said well casing, verticallylimited by positions of the upper feedthrough packer and the lowerfeedthrough packer.

The technical result is to ensure simultaneous flushing of theinter-packer annular gap between the well casing and the inventivedevice, as well as internal cavities of the inventive device after eachprocessed interval of the productive formation and to increase thereliability and manufacturability of the inventive device by simplifyingits design.

The technical result is achieved due to the fact that the method ofselective processing of the productive formation includes sequentialhydraulic fracturing and flushing of the inter-packer annular gap ofeach interval of the productive formation, using the inventive devicewhich is lowered into the well casing to the level of the lowestinterval of the productive formation.

When the inventive device reaches the level at which the interval of theproductive formation to be processed is located in the inter-packerannular gap, the inventive device is fixed to the well casing with themechanical anchor. Next, the working fluid is fed under pressure to thetubing, then to the hydraulic fracturing port, and the interval of theproductive formation is isolated with the packers which include cupsealing elements. Then hydraulic fracturing is carried out.

After hydraulic fracturing is finished, the inter-packer annular gap isflushed. During the first cycle, flush fluid is fed to the annularspace, then the lower feedthrough packer is activated and debris iswashed out of the upper area of the inter-packer annular gap throughwindows of the hydraulic fracturing port and up the tubing.

During the second cycle, the inventive device is turned to the transportposition. Then the tubing is axially moved to shift a hollow rod of theinventive device and flushing holes of the hydraulic fracturing port areopened. After that, the flush fluid is fed under pressure into thetubing, the cup sealing elements of the upper and lower feedthroughpackers are activated and the debris is washed out of the lower area ofthe inter-packer annular gap and the cup seals, pushing the mixturealong an inner cavity of the inventive device into the well casing.

Then the inventive device is moved to the next interval, whereprocessing and cleanup are carried out likewise.

The flush fluid is supplied by a pumping unit positioned on the surface.

To turn the inventive device to the transport position, the mechanicalanchor is deactivated by longitudinal movement of the inventive device.

Debris from the upper area of the inter-packer annular gap is disposedof on the surface in any known way.

The technical result is also achieved due to the fact that the inventivedevice comprises a mechanical anchor, a lower feedthrough packer, ahydraulic fracturing port, and an upper feedthrough packer sequentiallyinstalled on the tubing. The feedthrough packers with cup sealingelements are directed towards the hydraulic fracturing port. A hollowrod is located in the inner cavity of the inventive device.

A casing of the hydraulic fracturing port is divided by a partition intoan upper part with the aforementioned windows and a lower part with theaforementioned flushing holes, providing hydraulic connection of theannular inter-packer gap with the inner cavity in the lower part of thepartition. The lower feedthrough packer has a longitudinal cavity on theinner surface thereof, and the hollow rod features protrusions thatinteract with the longitudinal cavity while moving alongside. Thedistance between the lower feedthrough packer and the flushing holesdoes not exceed two diameters of the well casing.

The sealing capacity of the flushing holes is ensured by seals placedabove and below the flushing holes. The inner cavities of the hollowrod, the lower feedthrough packer and the mechanical collar locator forma single flushing channel. The hollow rod is rigidly bound to themechanical anchor.

The device can be additionally equipped with a collar locator positionedunder the lower feedthrough packer as well as with a centralizer.

Annulus flushing carried out in two cycles, during which debris isremoved from the upper or lower area of the annulus space, ensureshigh-quality cleanup.

Transporting debris from the inter-packer annular gap and disposing ofit at the surface during the first cycle, as well as removing debris outof the inventive device into a waste area of the well casing during thesecond cycle completely eliminates any solids.

The sequence of hydraulic fracturing, the first and second cycles of theinter-packer annular gap flushing ensures a smooth movement of thedevice along the casing.

The simple and reliable design of the device ensures the flow of theflush fluid through two unconnected debris removal channels, which aremanaged by a simple longitudinal movement (activation/deactivation) ofthe mechanical anchor and due to the interaction of two elements - thehollow rod and the body of the lower feedthrough packer.

DRAWINGS OF THE INVENTION

FIG. 1 - general view of the device;

FIG. 2 - enlarged view of the hydraulic fracturing port;

FIG. 3 - longitudinal section of the device in the transport position;

FIG. 4 - longitudinal section of the device with an activated mechanicalanchor;

FIG. 5 - enlarged view of the hydraulic fracturing port in the positionof the device shown in FIG. 3 ;

FIG. 6 - longitudinal section of the device during hydraulic fracturing;

FIG. 7 - working fluid flow diagram with an activated anchor; and

FIG. 8 - working fluid flow diagram with a deactivated mechanicalanchor.

DETAIL DESCRIPTION OF PREFERRED EMBODIMENT THE INVENTION

The present invention is designed for selective processing of aproductive formation in the oil mining industry. Generally, a boreholeassociated with the productive formation is provided and a well casing23 is mounted within the borehole. A tubing 22 is typically insertedinto the well casing 23. The inventive device essentially coupled withthe tubing 22 comprises: a mechanical anchor 1, a collar locator 2, alower feedthrough packer 3, a hydraulic fracturing port 4, an upperfeedthrough packer 5 and a centralizer 6 sequentially installed frombottom to top on the tubing 22 (FIG. 1 , FIG. 2 ). The mechanical anchor1 and the collar locator 2 each defines an inner cavity located therein.An annulus space is herein defined as a space between an outer surfaceof the inventive device / tubing 22 and, on the other hand, an innersurface of the well casing 23.

Pipes 7 are connected to the centralizer 6, the installation of which isdetermined by the need and conditions for processing intervals of theproductive formation of variable length.

The lower feedthrough packer 3 includes cup sealing elements 8 directedtowards the hydraulic fracturing port 4. The upper feedthrough packer 5includes cup sealing elements 9 also directed towards the hydraulicfracturing port 4.

The following well-known devices can be used as functional parts:

-   mechanical collar locator, which can be similar to the collar    locator A 1025-2, e.g. presented in the catalog “Tools for current    and major repairs of wells”, p. 31    <https://www.slb.ru/upload/iblock/d8e/katalog-instrumentov-dla-tekushego-i-kapitalnogo-remonta-skvaiin.pdf>);-   centralizer e.g. presented in    <http://www.coilsolutions.com/products/downhole-tools/drill-and-milling-tools/fluted-centralizers/>    or    <http://petrolibrary.ru/preduprezhdenie-iskrivleniya-vertikalnyix-skvazhi-skvazhin.html>;-   mechanically operated axial anchor (YAMO-3, YAMO-2), e.g. presented    in    <https://npf-paker.ru/catalog/type/yakorya/mekhanicheskie/yamo3-yamo2-yam3-yam2>.

A casing of the hydraulic fracturing port 4 includes windows 10 (FIG. 2). The hydraulic fracturing port 4 contains a partition 11 locatedinside the casing of the hydraulic fracturing port with a recess 12 inits lower part, and a divider 13 in the upper part (FIG. 3 ). Inaddition, radial flushing holes 14 are made in the lower part of thehydraulic fracturing port 4, connecting the recess 12 with the annulusspace.

The lower feedthrough packer 3 defines an inner cavity 19 within thereof(FIG. 7 ). A hollow rod 15 is at least partially located in the innercavity 19 of the lower feedthrough packer 3, with the possibility ofaxial movement, rigidly connected to the mechanical anchor 1 with a cone16. The hollow rod 15 defines its own inner cavity within thereof.

Sealing capacity of the radial flushing holes 14 is ensured by seals 18installed on an inner surface of the partition 11 above the holes 14 andon an inner surface of the lower feedthrough packer 3 below the holes14.

On a side of an outer surface of the hollow rod 15, it is equipped withlimiting protrusions 17 that perform axial movement along the cavity 19on the inner surface of the lower packer 3, the longitudinal size ofwhich determines a size S of a stroke of the hollow rod 15 (FIG. 3 andFIG. 4 ).

The inner cavity of the rod 15, the inner cavity of the lowerfeedthrough packer 3, the inner cavity of the collar locator 2 and theinner cavity of the mechanical anchor respectively communicate with eachother and form a single flushing channel 20 (FIG. 3 ).

When the device is set in a transport position, the hollow rod 15 is ina lower position, where the protrusions 17 rest against a lowerhorizontal wall of the cavity 18. The radial flushing holes 14 providecommunication of the recess 12 with the annular inter-packer space (FIG.2 and FIG. 3 ).

The cup seals 8 of the lower feedthrough packer 3 are located at adistance H1 (FIG. 3 ) from the flushing holes 14 of the hydraulicfracturing port 4; the distance H1 depends on a diameter of the wellcasing 23 and does not exceed two diameters of the well casing 23.

The device for implementing the described method works as follows:

Before lowering into the well casing 23, the device is assembled at thewellhead and installed on the tubing 22.

When descending, the mechanical anchor 1, the lower 3 and upper 5feedthrough packers are in the transport position, the hollow rod 15 isin the lower position and is fixed by the limiting protrusions 17 toprevent its axial downward movement.

Before processing the productive formation, the device is placed in ablank section of the well casing 23 and the feedthrough packers arepressed.

Next, the device is installed in such a way that the interval to beprocessed is located in the inter-packer space and the mechanical anchor1 is activated, ensuring that the device is fixed to the well withanchor elements 21 (FIG. 4 ). Then part of the tubing 22 weight isunloaded onto the mechanical anchor 1, while the hollow rod 15 entersthe recess 12, hermetically closing the flushing holes 14 with the helpof seals 18 (FIG. 5 ).

Next, hydraulic fracturing fluid is supplied to the tubing 22 underpressure and, due to the counterflow from the hydraulic fracturing port4, the cup sealing elements 8 and 9 of the feedthrough packers 3 and 5open and hermetically align to the inner wall of the well casing 23,reliably isolating the inter-packer space. Then, hydraulic fracturing isperformed (FIG. 6 ).

Upon hydraulic fracturing, the tubing 22, the inventive device and theannulus space between the device and the well casing 23 are flushed toremove proppant and other debris, ensuring a smooth and safe movement ofthe device to the next interval of the productive formation or duringits removal from the well casing 23.

Flushing of the annular space of the well casing 23 and the cavities ofthe device is carried out in two cycles as follows.

During the first cycle, the pumping unit located on the surface feedsthe flush fluid under pressure into the annular space, while the cupsealing elements 8 of the lower feedthrough packer 3 are in the activeposition. The flush fluid enters the inner cavity of the hydraulicfracturing port 4 through the windows 10 and then flows through theupper feedthrough packer 5 and up the tubing 22 to the surface, carryingthe proppant and other solids from the upper area of the inter-packerspace (FIG. 7 ). When the flushing technological period ends, the supplyof the flush fluid is stopped.

At the beginning of the second flushing cycle, the device is turned tothe transport position. To do this, the mechanical anchor 1 isdeactivated by longitudinal movement of the device. The hollow rod 15moves down until the limiting protrusions 17 rest against the wall ofthe cavity 19 and opens the flushing holes 14.

Then, the flush fluid is again fed under pressure into the tubing 22(FIG. 8 ). The flush fluid enters the internal cavities of the upperfeedthrough packer 5 and the hydraulic fracturing port 4. Then, it exitsthrough the windows 10 into the inter-packer space, activating the upper5 and lower feedthrough packers 3, thoroughly washing the proppant andother solids out of the lower area of the inter-packer space. Next, themixture enters the flushing holes 14 and the inner cavity of the rod 15.It then flows through a single flushing channel 20 outside the deviceinto the well casing 23.

The method is implemented as follows.

The inventive device assembled at the wellhead is lowered into the wellcasing 23, which is oppressed by a pressure of 15 MPa. The total lengthof the wellbore is 3250 m, including the sidetrack of 450 m. The deviceis lowered at a velocity of no more than 0.25 m/s when moving along thewell casing 23 with a diameter of 168 mm, a length of 2800 m, and at avelocity of 0.1 m/s when moving along a sidetrack with a diameter of 114mm (strength group N80 API 5CT).

First, the device is placed in a blank area of the sidetrack and thefeedthrough cup packers 5 and 3 are put under 12 MPa pressure.

The sequence of productive formation interval processing is set in sucha way that the lowest interval at the level of 3200 - 3215 m isprocessed first.

The inventive device is installed in the well casing 23 in such a waythat the interval to be processed is located between the cup packers 5and 3. The inventive device is then fixed to the well casing 23 withanchor elements 21 when the mechanical anchor 1 is activated (FIG. 4 ).

Next, the hydraulic fracturing fluid is pumped through the tubing 22 andpackers 5 and 3 with cup seals 8 and 9 are activated, ensuring a tightfit to the inner wall of the well casing 23 and reliably isolating theannular gap between the well casing 23 and the inventive device in theinter-packer space. Then hydraulic fracturing is carried out at 46 MPa.(FIG. 6 ).

At the end of hydraulic fracturing, the hydraulic fracturing fluidsupply is stopped. Meanwhile, debris, including proppant, accumulates inthe inter-packer annular gap and in the cup seals, which can lead to theinventive device jamming when moving to the next formation interval tobe processed.

To prevent an emergency, the inter-packer annular gap is flushed toremove debris (mechanical particles, proppant) after hydraulicfracturing.

The first cycle begins with supplying the flush fluid at 100 atmospheresby a pumping unit located on a ground surface surrounding a top entrance(top mouth) of the well casing 23. Ensuring the flow rate of the flushfluid of 6 1/s, the cup seals 8 of the lower feedthrough packer 3 areactivated. The debris is washed out of the upper area of theinter-packer annular gap through the windows 10 of the hydraulicfracturing port 4, being pushed along the tubing to the surface fordisposal (FIG. 7 ).

After removing debris from the upper area of the inter-packer annulus,the flush fluid supply is stopped.

During the second washing cycle, the mechanical anchor 1 is deactivatedby longitudinal movement of the device, and the device is turned to thetransport position. Next, the tubing 22 is axially moved to shift thehollow rod 15 of the device until the limiting protrusions 17 restagainst the wall of the cavity 19 opening the flushing holes 14. Then,the flush fluid is supplied at a pressure of 12 MPa and at a flow rateof 1.5 1/s, activating the lower 3 and upper 5 packers.

Moving through the opened flushing holes 14 through a single flushingchannel 20, the flush fluid cleans the lower area of the inter-packerannulus. It washes out small debris from the cup seals 8 of the lowerpacker 3 and all the internal cavities of the device below the hydraulicfracturing port, while all the debris is pushed down outside the deviceinto the well casing 23. The cleanup period of the second cycle isdetermined by the presence or absence of resistance to the movement ofthe device in the well casing 23.

After it is flushed, the device is lifted to process the second intervalof the productive formation at the level of 3035 - 3050 m observing thesequence of actions for hydraulic fracturing and flushing of the annularinter-packer space and the elements of the device.

After the third interval (2870 - 2885 m) is processed and flushed, theinventive device is removed from the well casing 23.

Thus, the claimed invention makes it possible to provide high-quality,technological cleanup of the inter-packer annulus space, trouble-freemovement of the downhole tool for processing several intervals of theproductive formation within one tripping, using a simple and reliabledevice.

1. A device for selective processing of a productive formationessentially coupled with a tubing insertable into a well casingassociated with the productive formation; said well casing defines aninner sidewall surface thereof and has a diameter; said tubing definesan outer surface thereof; said device defines an outer surface thereof;wherein an annulus space is defined to include: a space between theouter surface of said device and the inner surface of said well casing,and a space between the outer surface of said tubing and the innersurface of said well casing; wherein said device comprises sequentiallymounted on the tubing from bottom to top: a mechanical anchor; a collarlocator; a lower feedthrough packer equipped with a number of cup seals;said lower feedthrough packer defines a lower packer inner cavityprovided therein; said lower feedthrough packer has a hollow rod capableof axial movement at least within the inner cavity of said lowerfeedthrough packer; said hollow rod is partially passed through thecollar locator, and partially passed through and rigidly connected tothe mechanical anchor; a hydraulic fracturing port divided by apartition into an upper part including an upper cavity provided withwindows and a lower part provided with a recess and flushing holescommunicated with the recess; said number of cup seals of the lowerfeedthrough packer are directed towards the hydraulic fracturing port;an upper feedthrough packer equipped with a number of cup seals directedtowards the hydraulic fracturing port; and a centralizer; wherein: aninter-packer annular gap is defined as a portion of the annulus spacelocated between the outer surface of said device and the inner sidewallsurface of said well casing, vertically limited by positions of theupper feedthrough packer and the lower feedthrough packer; said flushingholes provide for hydraulic connection of the inter-packer annular gapwith said recess in the partition lower part; and wherein: a distancebetween the lower feedthrough packer and the flushing holes does notexceed said diameter of the well casing multiplied by two.
 2. The deviceaccording to claim 1 wherein seals placed above and below the flushingholes.
 3. The device according to claim 1, wherein said hollow roddefines a rod inner cavity within thereof; said collar locator defines acollar inner cavity within thereof, and wherein the rod inner cavity,the lower packer inner cavity and the collar inner cavity form a singleflushing channel.
 4. A method for selective processing of the productiveformation using the device according to claim 1; wherein the productiveformation includes a number of intervals; said method comprising thesteps of: lowering the tubing with the device to a lowest intervalchosen from said number of intervals; setting up the lowest intervalwithin the inter-packer annular gap; fixing the device to the wellcasing by the mechanical anchor; supplying working fluid under pressureinto the tubing and into the hydraulic fracturing port; isolating thelowest interval by said number of cup seals of the lower feedthroughpacker and said number of cup seals of the upper feedthrough packer;providing hydraulic fracturing of the lowest interval by the workingfluid; feeding the flush fluid into the inter-packer annular gap;activating the lower feedthrough packer and washing debris out of anupper portion of the inter-packer annular gap through said windows ofthe hydraulic fracturing port and up the tubing; turning the device intoa transport position; axially moving up the tubing thereby shifting thehollow rod and opening the flushing holes; feeding the flush fluid underpressure into the tubing; activating said number of cup seals of thelower feedthrough packer and said number of cup seals of the upperfeedthrough packer and washing debris out of a lower portion of theinter-packer annular gap and pushing a mixture of the flush fluid andthe debris mixture along said inner cavity of the device into the wellcasing; moving up the device to a next interval chosen from said numberof intervals, and repeating the steps above.
 5. The method according toclaim 4 wherein said well casing defines a top entrance thereof and aground surface surrounding the top entrance, and wherein the flush fluidis supplied by a pumping unit positioned on the ground surface.
 6. Themethod according to claim 4 wherein the step of turning the device intothe transport position is provided by deactivation of the mechanicalanchor.
 7. The method according to claim 4 wherein said well casingdefines a top entrance thereof and a ground surface surrounding the topentrance; and wherein the debris froman upper portionof the inter-packerannular gap is pushed up along the tubing and being disposed of on theground surface. 8-9. (canceled)